This invention relates to a liquid crystal display device for an overhead projector and more particularly to a liquid crystal display device for forming an image therein by using a personal computer or the like such that an enlarged display image thereof can be projected on a screen by means of an overhead projector.
As shown in FIG. 5, a conventional liquid crystal display device 51 for an overhead projector typically includes a light-transmissive liquid crystal display cell 52 with its upper and lower surfaces covered by protective filters 53 and 54 and a liquid crystal display panel 55 thus formed is supported in a horizontal position by a cabinet 56. Light is projected from below and passed through the liquid crystal display panel 55 such that an image formed on the display cell 52 is enlarged and projected onto a screen (not shown) by means of an optical system (not shown). Numerals 57a and 57b indicate circuits for operating the liquid crystal display cell 52.
With a conventional display device 51 thus structured, one cannot ignore the problem of controlling the rise in the temperature of the display cell 52 caused by the light beam. If the intensity of the light is too strong, the cell 52 becomes too hot and the contrast and color in the displayed image tend to become uneven. If the light is too weak, on the other hand, the projected image on the screen becomes too dark for clarity.